G&G RK104 Battery.
 

In the manual says recommended battery type should be a 8.4v 1800mah battery Ive got 3 1600 mini's and a got a large 1.2v 5000mah. Would it be safe to use that??

Yes those would be fine. Although I'm pretty sure your large isn't 1.2V, unless it's a single cell.

okay thanks, thing is i dont have a soldier. Need to replace the small tamyia for a large..